Electronically scannable directional antenna



July 14, 1964 p. .1. KAHRILAs 3,141,165

ELECTRONICALLY SCANNABLE DIRECTIONAL ANTENNA 2 Sheets-Shea?. 1

Filed Aug. 12, 1960 July 14, 1964 P. J. KHRILAS ELECTRONICALLY SCANNABLE DIRECTIONAL ANTENNA Filed Aug. 12, 1960 2 Sheets-Sheet 2 HET DUPLEXER CONVERTER 5 54 fTfE H T 28 PowER E AMP. CONVERTER 'RCULATOR I Moo. PULSE r F l G. 2

j`58 cmcuLAToR 650 59 f f HET. HET. f -f E A yCQNVERTER coNvERTER E clRcuLAToR 1a --umomsu-QQMQJ--n- T 1g T t T INVENTOR ATI'ONEY E United States Patent O 3,141,165 ELECTRONICALLY SCANNABLE DIRECTIONAL ANTENNA Peter J. Kahrilas, Roslyn, N.Y., assignor to Sperry Rand Corporation, Great Neck, N.Y., a corporation of Delaware Filed Aug. l2, 1960, Ser. No. 49,364 5 Claims. (Cl. 343-100) The present invention generally relates to antennas for the directional radiation and reception of electromagnetic energy and, more particularly, to such antennas adapted for the essentially instantaneous alteration of beam direction.

The recent rapid development of the air and space flight arts has sharply increased the need for rapidly scannable directional antennas. In certain applications such as aircraft trafiic control, it is primarly the increased density of traffic which requires that the surveillance radar beam be rapidly slewed from one direction to another so that an adequate data rate may be maintained on a large plurality of independently maneuvering aircraft targets. In other instances, the relatively great target velocities necessitate the rapid alteration of antenna beam position. Of course, both conditions of increased target velocities and increased target density may be encountered simultaneously in a given situation.

Electronically scannable directive arrays have been proposed to reduce the time required to change beam position. Although substantial improvement has been accomplished relative to the mechanical and electromechanical antenna scanning arts, the enhancement of scanning rates so far obtained does not provide an adequate margin in contemplation of more demanding future requirements.

Generally speaking, any technique for electronic scanning is limited in accordance with the dynamic response characteristic (inertia) of the device which controls beam direction. For example, consider the case where an electronically scannable beam is produced by a series of radiating elements connected in cascade and excited by a signal of given frequency. The exciting signal ows from one radiating element to the next through respective phase shift devices which interconnect adjacent ones of the elements. The direction of the beam produced by the array of radiating elements is controlled by adjustment of the phase shift devices which determines the relative pbase between the signals radiated from adjacent elements. Of course, the maximum rate at which the direction of the beam may be changed depends upon the minimum time which is required to effect changes in the phase shift produced by the phase shift devices. Where ferrites are employed in the phase shift devices, said minimum time may be of the order of a few microseconds for low power levels or milliseconds for high power levels. The adequacy of such response depends upon the system and range requirements being encountered and may be less than desired where high speed and high density target operations are involved.

It is the principal object of the present invention to provide an electronically scannable directive antenna characterized by the ability of having its beam direction rapidly altered.

Another object is to provide wide band means for varying the relative phase between signals radiated from an adjacent pair of elements in a directive antenna array.

A further object is to provide highly efficient and stable means for electronically controlling the directive axis of an antenna.

An additional object is to provide an electronically scannable antenna whose directive axis may be controlled 3,141,165 Patented July 14, 1964 ice along one or more coordinates independently of the frequency of the signals radiated or received by said antenna.

Another object is to provide an electronically scannable directional antenna adapted for passively determining the direction of a source of incoming signals.

These and other objects of the present invention as will appear from a reading of the following specification are accomplished in a preferred embodiment by the provision of a two coordinate directive array of microwave signal radiating elements. The elements are connected along row and column positions by wide band variable phase shift devices of a heterodyne converter type. The devices operate on the principle that a selected side band output signal of a heterodyne converter is shifted through precisely the same phase angle as the phase angle through which one of the two input signals is shifted. Thus, the phase angle information contained in the input signal is preserved in the output signal despite the fact that the input and output signals are not of the same frequency.

By properly exploiting the wide band properties of the heterodyne converter phase shift devices the relative phase between the signals radiated by each adjacent pair of radiating elements of the present invention may be varied in an extremely short time interval. The directive axis of the composite beam resulting from all the elements may be controlled along two axes such as elevation and azimuth by separately controlling the relative phase be* tween the adjacent column-connected elements and the adjacent row-connected elements. A feature of the in vention is that the frequency of the signals radiated from the elements may be varied independently of the relative phase between the signals radiated from adjacent pairs of elements.

For a more complete understanding of the present invention, reference should be had to the following specification and to the figures of which:

FIG. 1 is a simplified block diagram of a preferred embodiment of an electronically scannable directive antenna constructed in accordance with the invention;

FIG. 2 represents the functional block details of one of the phasing devices used in the apparatus of FIG. l; and

FIG. 3 represents the functional block details of another of the phasing devices used in the apparatus of FIG. 1.

Referring to FIG. l, individual radiating elements 1-9 are arranged in the conventional row and column positions of a directional antenna array. Although only nine elements are shown by way of example, it will be understood that a greater or lesser number of elements may be employed depending upon the directivity desired of the beam resulting from the individual contributing elements. As is well understood in the art, the direction of the resultant beam is dependent upon the relative phase beween the signals radiated from adjacent ones of the elements. For example, the elevation position of the resultant beam is a function of the phase angle between the vertically arranged elements such as elements 4, 5 and 6 whereas the azimuth position of the resultant beam is a function of the phase angle between the horizontally arranged elements such as elements 2, 5 and 8.

As will be described later, the elevational phasing of the elements is determined by the frequency (fE) of the signal generated by generator 10; azimuthal phasing is determined by the frequency (fA) of the signal generated by generator 11. However, neither of the JE and JA frequencies have any effect on the frequency of the signals radiated by the elements 1-9. The frequencies at which generators 10 and l1 are operable is controlled by signals respectively applied to lines 12 and 13.

The output signal of generator 1l is applied via gate 14, when conducting, to the input terminal of a conventional tapped delay line 15. Delay line may be either of the lumped constant or distributed type as is suited to the frequency fA of the signal generated by generator 11. Delay line 15 is terminated by a characteristic impedance termination 16. The taps 17, 18 and 19 are located along delay line 15 at equal electrical length intervals. Each of said taps is connected to a respective one of the bilateral heterodyne converters 20, 21 and 22.

The details of a suitable bilateral heterodyne converter will be explained in connection with FIG. 3. For the present, it will be sufficient to merely state that one of the functions of each of the converters 20, 21 and 22 is to beat the signal of frequency fA present at a respective one of the taps 19, 18 and 17 with a second signal having a frequency of fE-fA. A signal having a frequency fE-JA is produced at the output of heterodyne converter 23 to which generators 11 and 10 are connected. The upper side band resulting from the heterodyning of the fE-JA and fA signals is filtered out and made available at the output of each of the bilateral heterodyne converters. The converters are bilateral in the sense that the fE-JA signal will beat with a signal applied to either one of the two additional terminals toproduce a side band component at the other of the additional terminals.

If the signal passed by gate 14 is designated fA then the signals present at taps 18 and 19 may be designated, respectively, fA+A and fA-l-nqpA where A represents the phase shift introduced by each delay line segment and n represents the number of delay segments. Consequently, a signal of frequency JE is produced at the output of converter 22, a signal of frequency fg at the phase angle qbA designated fE--qbA is produced at the output of converter 21 and a signal fE+nA is produced at the output of converter 20. The signal fE is applied to the input of vertically disposed delay line 24, the signal fE-{- A is applied to a similarly disposed delay line 25 and the signal fE-l-nqbA is applied to the corresponding delay line 26. It should be noted that only the phase angle A between the signals at taps 17, 18 and 19 remains in the signals which excite the vertically disposed delay lines 24, 25 and 26. Each of the delay lines 24, 25 and 26 is tapped at equal delay intervals to produce the indicated signals at taps 27, 28 and 29.

Each of the taps of each of the vertically disposed delay lines 24, 25 and 26 is connected to a respective bilateral heterodyne converter and power amplifier such as designated by blocks 30, 31 and 32. A typical bilateral heterodyne converter and power amplifier will be described in connection with FIG. 2. Briefiy, the function of each one is generally similar to that of converters 20, 21 and 22 with the exception that power amplification is additionally acomplished when signal flow is directed from the respective delay line junction to the associated radiating element. The power amplifier contained within each converter is actuated by an applied modulating pulse. A signal having the frequency fT-E is also applied to each converter and power amplifier unit. A signal at frequency fT is produced by generator 33 whose output is connected to a first input of heterodyne converter 34. Generator 10 is connected to a second input of converter 34. Converter 34 produces the required signal at frequency fT-E.

Signals at frequencies fE and fT-fE are applied to converter 32 to produce an amplified upper sideband signal at frequency fT which is radiated from element 9. Similarly, a signal at frequency fT and relative phase angle A is produced at `the output of converter 31 and radiated from element 6 whereas a signal at frequency fT and phase angle mpA is produced at the output of converter 30 and applied to radiating element 3. It can be seen that the signals radiated from the successive vertically disposed elements 7, 8 and 9 will each be at the same frequency T but will successively differ from each other in phase angle by the amount qbE. The signals radiated from the successive vertically disposed elements 4, 5 and 6 will also be at the same frequency fT and will successively differ by the phase angle E but in addition, will differ in phase from the signals radiated by elements 7, 8 and 9 by a fixed amount 115A. Said fixed amount is interposed by the delay line 1S between taps 17 and 18.

The frequencies and relative phases of the signals present at various points in the system for exciting the array of elements 1-9 are indicated in FIG. 1. As is well understood in the art, the relative phasing between the adjacent elements determines the direction of the resultant beam produced by the array. In accordance with the present invention the frequencies fA and fE respectively determine the azimuthal and elevational phasing of the elements comprising the array whereas the frequency of the signals radiated from said elements is determined exclusively by the frequency fT produced by generator 33.

When frequency fA is changed, for example, the phase angle between the signals at each of the taps 17, 18 and 19 will also change. The wide band properties of converters 20, 21 and 22, permit the changed phase angle between the fA signals at junctions 17, 18 and 19 to appear essentially instantaneously between the signals at frequency fE at the outputs of converters 22, 21 and 20. The same phase angle shift between the signals at the outputs of converters 22, 21 and 20 will also essentially instantaneously be introduced between the signals at frequency fT at the outputs of converters 32, 31 and 30. Similar action takes place at the outputs of converters 35-40.

It should be noted that the phase angle between the signals at frequency fT radiated from an adjacent pair of elements, for example elements 5 and 8, is independent of the frequency fT-fE of the signal applied to converters 36 and 37. That is, by changing the frequency of the signal produced by generator 33 only the frequency of the signals radiated from elements 5 and 8 is changed. The relative phase angle 41A obtaining between the signals radiated from elements 5 and 8 is unchanged. The angle A is determined exclusively by the frequency fA of the signal produced by generator 11. Likewise, a shift in frequency f-I- will not alter the relative phase angle ,bE between the signals radiated by the adjacent elements. The phase angle QSE is determined exclusively by the sig nal generated by generator 10.

When the pulsed electromagnetic energy radiated by the array is refiected from a target object and received by the elements 1-9, it is heterodyned with a signal at frequency fT-E in each of the converters 30, 31 and 32 and 35-40. The signal conversion system is entirely reciprocal in operation whereby a signal at frequency fE is produced at each tap of the vertically disposed delay lines 24, 25 and 26 in response to the target-reflected energy. The received signals then propagate downwardly through each of the delay lines 24, 25 and 26 and the associated converters 22, 21 and 20 to the respective junctions 17, 18 and 19 along delay line 15. All of the received signals then recombine at tap 17 in proper phase.

The combined signals are applied via gate 41, when conducting, to a rst input of heterodyne converter 42. Gates 41 and 14 are actuated in alternation by multivibrator 43, i.e., gate 41 is rendered conductive and gate 14 is non-conductive and vice versa. Multivibrator 43, in turn, is triggered at the radar repetition rate slightly in advance of the pulsing of the power amplifiers associated with converters 30, 31 and 32 and 35-40. The time interval between the triggering of multivibrator 43 and the pulsing of the power amplifiers is determined by delay 44 through which the multivibrator trigger pulse passes to produce the modulator actuating pulse on line 45. The inputs to delay 44 and multivibrator 43 are connected to the radar pulse repetition rate generator contained within programming circuit 46.

Multivibrator 43 is of the monostable type. It is placed into its unstable condition by each system trigger pulse derived from programming circuit 46 and remains in said condition for a brief period of time sufiicient to allow for the ow of the fE and fA signals through the respective delay lines 24, 25, 26 and 15 and for the radiation of signals by elements 1-9. Gate 14 is rendered conductive during this interval. At the close of said interval, multivibrator 43 reverts to its stable condition closing gate 14 and opening gate 41 to permit the passage of received target reflected signals through gate 41.

As previously mentioned, the received signals passing through gate 41 are applied to a first input of heterodyne converter 42. A locally generated signal at frequency fA-t-flp is applied to second input of converter 42. The resulting IF signal is amplified in amplifier 47 and applied to an ordinary detector and target indicator 48. Detector and indicator 48 includes a conventional sweep generator and cathode ray tube for the display of received target signals. The sweep generator is triggered synchronously with the radiation of signals by elements 1-9 by the synchronizing pulses of line 45. The local signal at frequency fA-l-fIF is produced at the output of heterodyning converter 49 to which fIF generator 50 and fA generator 1l are connected.

In a representative case, the frequencies of the signals produced by generators and 11 may be varied in a predetermined manner so as to produce raster scanning of the resultant beam radiated by the directional array. Such raster scanning of the radiated beam may be achieved by the provision of sweep generating circuits within programming circuit 46 similar to the ones included in ordinary television receivers for horizontal and vertical defiection. The two sweep potentials are applied by respective lines 12 and 13 to generators 10 and 11 to vary the frequency of the fE and A signals. The individual sweep voltages of lines 12 and 13 are synchronized with respect to the radar repetition interval by the action of programming circuit 46. It should be noted, however, that the specific manner in which frequencies fA and fE are varied by the action of programming circuit 46 is immaterial to the present invention.

Each of the bilateral heterodyne and power amplifiers 30, 31 and 32 and 35-40 may be of the type represented in FIG. 2. Typical converter 36 of FIG. 2 comprises a conventional circulator 52 having a first input connected to tap 28 along delay line 25 of FIG. 1. The signal applied to circulator 52 from tap 28 is routed exclusively to a first input of heterodyne converter 53, second input to which is the signal at frequency fT-E. The signal present at tap 28 is at frequency fE as previously described. The resultant side band at frequency fT is selected and applied to power amplifier 54. Amplifier 54 is actuated by the modulating pulse derived from line 45 of FIG. 1 to produce an amplified pulse of energy at carrier frequency fT for application to duplexer 55. The amplified pulse energy is then radiated by element 5.

Echo pulses of carrier frequency fT reected from target objects are received by element 5 and routed exclusively to a first input of heterodyne converter 56. A signal at frequency fT-E is also applied to converter 56 to produce an output signal at frequency fE. Said output signal is applied via circulator 52 to tap 28 of delay line 25.

A typical bilateral heterodyne converter such as converter 21 of FIG. 1 is shown in FIG. 3. Illustrative converter 21 comprises circulators 57 and 58, and conventional heterodyne converters 59 and 60. The first input of circulator 57 is connected to tap 18 along delay line 15. A signal at frequency IA is applied via circulator 57 to a first input of heterodyne converter 59. A signal at frequency fE-A is applied to a second input of converter 59. The resultant side band signal at frequency fE is selected and applied to a first input of circulator 58 through which it is directed to converter 31 and the input 61 to delay line 25 of FIG. l.

In the case of received signals reflected from target objects, the received signal at frequency fE propagates downwardly in the view of FIG. 1 along delay line 25 as previously explained. Said received signal is applied via line 61 and circulator 58 to heterodyne converter 60. A signal frequency fE-A is also applied to converter 60. The resultant side band signal at frequency fA is selected and applied via circulator 57 to tap 18 of delay line 15.

It can be seen from the preceding specification that the objects of the present invention have been achieved through the use of wide band phase shifting means of the heterodyne type to controllably vary the relative phase between signals radiated from the adjacent elements of a directive antenna array. By virtue of the wide band properties of the phase shifting means, the directive axis of the antenna beam may be altered essentially instantaneously in response to the variation in frequency of a control signal. In the case of a two dimensional array first and second control signals (A and fE) respectively determine the azimuth and elevation coordinates of the directive axis of the antenna array. A feature of the invention also attributable to the use of the heterodyning technique is that the direction of the antenna beam may be controlled independently of the frequency of the signals which are radiated and received.

It should also be noted that the scannable antenna of the present invention may be readily adapted for the passive detection of incoming signals where the direction of the source of said incoming signals is to be determined. For this purpose, it is preferred to provide an auxiliary receiving antenna such as, for example, a microwave horn which is broadly directive throughout approximately the same total volume as is scanned by the array antenna of FIG. 1. The function of the auxiliary antenna is to provide `a source of signals at the frequency of the incoming energy for application to heterodyne converter 34 of FIG. 1 in lieu of the signal produced by fT generator 33. After such signal substitution has been made, then it is merely necessary that the frequency of the signals produced by generators 10 and 11 be varied under the direction of programming circuit 46 in the same manner as required for scanning during transmission. When a maximum indication is produced by indicator 48, it can be concluded that the coordinates of the direction of the incoming signals corresponds to the frequency values of the signals produced by generators l0 and 11 at the time when said maximum indication results.

While the invention has been described in its preferred embodiments, it is understood that the words which have been used are words of descripiton rather than of limitation and that changes within the purview of the appended claims may be rnade without departing the true scope and spirit of the invention in its broader aspects.

What is claimed is:

1. In a scannable directional antenna array, means for scanning the directive axis of said array by controlling the phase angle between the signals radiated or received by adjacent ones of the radiating elements comprising said array, said means including a first signal delay line, a source of first signals connected to the input of said first delay line, a plurality of first heterodyne converters each being connected to said first delay line at respective points, a source of second signals having a frequency differing from the frequency of said first signals, means for applying said second signals to each of said first converters, a plurality of second signal delay lines, the input of each said second delay lines being connected to the output of a respective one of said first converters, a plurality of second heterodyne converters each being connected to a respective one of said second delay lines, a source of third signals having a frequency differing from the frequency of said second signals, means for applying said third signals to each of said second converters, means for coupling the output of each of said second converters to a respective one of said radiating elements, and means for changing the frequency of one of said first and second signals.

2. In a scannable directional antenna array, means for scanning the directive yaxis o-f said array by controlling the phase angle between the signals radiated or received by adjacent ones of the radiating elements comprising said array, ysaid means including a first delay line tapped at substantially equal electrical length intervals, a source of first signals connected to the input of said first delay line, a plurality of first heterodyne converters cach being connected to a respective tap along said first delay line, a source of second signals having a frequency differing from the frequency of said first signals, means for applying said second signals to each of said first converters, a plurality of second tapped delay lines, the input of each said tapped delay line being connected to the output o-f a respective one of said first converters, a plurality of second heterodyne converters, each tap along each said second tapped delay line being connected to a respective one of said second converters, a source of third signals having a frequency differing from the frequency of said second signals, means for applying said third signals to each of said second converters, means for coupling the output of each of said second converters to a respective one of said radiating elements, `and means for varying the frequency of one of said first and second signals.

3. Apparatus as defined in claim 2 wherein each said means for coupling the output of each of said second converters to a respective one of said radiating elements includes pulsed amplifier means.

4. Apparatus as defined in claim 2 and further including first means for selectively connecting when actuated said source of first signals to the input of said first delay line, a signal receiver, second means for selectively connecting said input of said first delay line to said signal receiver, and means for alternatively actuating said first and second selectively connecting means.

5. In a scannable directional antenna array, means for scanning the directive axis of said array by controlling the phase angle between the signals radiated or received by adjacent ones of the radiating elements comprising said array, said means including a first delay line tapped at substantially equal electrical length intervals, a source of first signals connected to the input of said first delay line, a plurality of first bilateral heterodyne converters, each tap along said first delay line being connected to a respective one of said first converters, a second heterodyne converter, a source of second signals, said first and second signals being applied to said second converter, said second converter producing a first output signal having a frequency equal to the difference between the frequencies of said first and second signals, means for applying said first output signal to cach of said first converters, a plurality of second tapped delay lines, the input of each said second delay line being connected to the output of a respective one of said first converters, a plurality of third bilateral heterodyne converters, each tap along each said second delay line being connected to a respective one of said third converters, a source of third signals, a fourth heterodyne converter, means for applying said second and third signals to said fourth converter, said fourth converter producing a second output signal having a frequency equal to the difference between the frequencies of said second and third signals, means for applying said second output signal to each of said third converters, means for coupling the output of each said third converter to a respective one of said radiating elements, and means for varying the frequency of said first and second signals.

References Cited in the file of this patent UNITED STATES PATENTS 2,409,944 Loughren Oct. 22, 1946 2,680,151 Boothroyd June 1, 1954 3,005,960 Levenson Oct. 24, 1961 

1. IN A SCANNABLE DIRECTIONAL ANTENNA ARRAY, MEANS FOR SCANNING THE DIRECTIVE AXIS OF SAID ARRAY BY CONTROLLING THE PHASE ANGLE BETWEEN THE SIGNALS RADIATED OR RECEIVED BY ADJACENT ONES OF THE RADIATING ELEMENTS COMPRISING SAID ARRAY, SAID MEANS INCLUDING A FIRST SIGNAL DELAY LINE, A SOURCE OF FIRST SIGNALS CONNECTED TO THE INPUT OF SAID FIRST DELAY LINE, A PLURALITY OF FIRST HETERODYNE CONVERTERS EACH BEING CONNECTED TO SAID FIRST DELAY LINE AT RESPECTIVE POINTS, A SOURCE OF SECOND SIGNALS HAVING A FREQUENCY DIFFERING FROM THE FREQUENCY OF SAID FIRST SIGNALS, MEANS FOR APPLYING SAID SECOND SIGNALS TO EACH OF SAID FIRST CONVERTERS, A PLURALITY OF SECOND SIGNAL DELAY LINES, THE INPUT OF EACH SAID SECOND DELAY LINES BEING CONNECTED TO THE OUTPUT OF A RESPECTIVE ONE OF SAID FIRST CONVERTERS, A PLURALITY OF SECOND HETERODYNE CONVERTERS EACH BEING CONNECTED TO A RESPECTIVE ONE OF SAID SECOND DELAY LINES, A SOURCE OF THIRD SIGNALS HAVING A FREQUENCY DIFFERING FROM THE FREQUENCY OF SAID SECOND SIGNALS, MEANS FOR APPLYING SAID THIRD SIGNALS TO EACH OF SAID SECOND CONVERTERS, MEANS FOR COUPLING THE OUTPUT OF EACH OF SAID SECOND CONVERTERS TO A RESPECTIVE ONE OF SAID RADIATING ELEMENTS, AND MEANS FOR CHANGING THE FREQUENCY OF ONE OF SAID FIRST AND SECOND SIGNALS. 